June 7, 2021
The clinical approval of biological therapeutics inhibiting CTLA-4 (ipilimumab), PD-1 (nivolumab, pembrolizumab) and PD-L1 (atezolizumab, avelumab, durvalumab) has ushered in a revolution in the field of cancer immunotherapy. Thus far, the approvals have occurred in a small number of cancer histotypes including melanoma, non-small cell lung cancer and urothelial cancers, but over 2000 active clinical trials of these drugs are ongoing. The common mechanism of action that links these agents together is that they target T cell checkpoint pathways. The role of T cell checkpoint receptors is to down-regulate T cell proliferation and effector function after these processes have been initiated by stimulation of T cells via the T cell receptor (TCR) and CD28, the primary T cell costimulatory receptor.